Turbine engines have circular arrays of airfoils on rotating disks in both the compressor section and the turbine section of the engine. The airfoils are radially oriented with respect to the rotation axis, and are closely surrounded by a shroud that defines an outer envelope for the flow path of the working gas (air or combustion gases). The greater the clearance between the blade tips and shroud, the less efficient is the conversion of energy between the working gas and the rotating disk, since some of the working gas leaks over the airfoil tip. This clearance varies under differing operating conditions such as engine startup due to differential thermal expansion, thus making it hard to control the leakage. Much effort has been made to minimize this clearance, including reducing it so much that the blade tips occasionally touch and abrade the shroud. Some designs dynamically control the shroud diameter during engine operation.
Plasma generators have been used on aerodynamic components of turbine engines to influence boundary layers in various ways. For example US patent publication 2009/0169356 describes generating plasma in the tip-to-shroud clearance for aerodynamic stabilization. US patent publication 2008/0089775 describes reducing the effective tip-to-shroud clearance by filling it with plasma. A type of plasma generator often used in these efforts is called a dielectric barrier plasma generator, in which one electrode is covered with insulation and a second electrode is exposed to the intervening gas. This type of plasma generator is described for example in U.S. Pat. No. 7,380,756, which describes that airflow is induced by the plasma in a direction from the exposed electrode to the covered electrode when an alternating voltage is applied between the electrodes.